QXmlInputSource misuses QIODevice and doesn't behave according to its own documentation

/*!
    Constructs an input source and gets the data from device \a dev.
    If \a dev is not open, it is opened in read-only mode. If \a dev
    is 0 or it is not possible to read from the device, the input
    source will contain no data.

    \sa setData() fetchData() QIODevice
*/
QXmlInputSource::QXmlInputSource(QIODevice *dev)
{
    init();
    d->inputDevice = dev;
    d->inputDevice->setTextModeEnabled(false);
}

if (!dev->isOpen())
    dev->open(QIODevice::ReadOnly);